FIELD OF THE INVENTION
[0001] This invention relates to mechanical seal assemblies and particularly to bellows
mechanical seal assemblies having an improved arrangement for attaching a hard faced
seal ring and its supporting means to the bellows, permitting the use of high temperature,
corrosion resistant alloys with non-weldable seal rings, and avoiding the use of interference
and/or lap joint fits between a seal ring and its supporting flange.
BACKGROUND OF THE INVENTION
[0002] Mechanical seal assemblies are conventionally used in fluid handling apparatus, such
as pumps and the like, to substantially prevent the leakage of process fluid, which
may be corrosive, along a shaft to the motor or bearing system which drives the apparatus.
Such leakage could seriously affect the motor or bearing system and probably cause
its destruction. Mechanical seal assemblies generally are constructed with a pair
of seal rings, one connected to and rotatable with the shaft, and the other, non-rotatable
and connected to the housing and the like. Each seal ring is provided with a lapped
seal face, the seal faces of the rings oppose one another in engaging relationship,
and rotate relative to one another. At least one of the seal rings is constructed
of a relatively hard, non-weldable material, such as silicon carbide, tungsten carbide
and the like, while the other seal ring is constructed of a similar or different material
which could be silicon carbide, a graphitic material and the like. Means, such as
springs, bellows and the like are employed to urge the seal faces in rubbing contact
with one another. A slight leakage of fluid, which may be supplied to the seal faces,
cools and lubricates the relatively rotating and engaging seal faces to prolong their
useful operating life.
[0003] The rubbing contact between the seal faces of mechanical seals and the wear characteristics
of seal rings dictates the use of relatively hard materials for the seal rings, such
as the aforesaid silicon carbide and the like. The attachment and sealing of these
hard materials to the supporting structure of the assembly is dependent upon the material
used, the particular arrangement of components, and the operating conditions of the
assembly. In some assemblies, a secondary elastomeric seal, such as an elastomer O-ring
is used between the seal ring and its supporting structure, as for example, a support
flange. In high temperature apparatus, on the order of 500 degrees F. and above, a
secondary elastomeric seal between a seal ring and its supporting structure cannot
be used because of the temperature limitations of the elastomeric material. Traditionally,
high temperature mechanical seals have utilized lap joints or mechanical interference
fits between the seal ring and its supporting structure constructed of low expansion
alloy materials. The lap joint arrangement functions well, but is very maintenance
intensive and critical due to dirt contamination during assembly. Lower expansion
alloy seal ring supporting structure-seal ring interference fits are also functional;
however, because the lower expansion alloys characteristically have low corrosion
resistance, they are not compatible with high temperature and corrosive fluids and
fail rapidly, necessitating repair and/or replacement. The repair and/or replacement
of a mechanical seal assembly is a costly procedure requiring considerable down time
of the fluid handling apparatus with loss of productivity.
DISCUSSION OF PRIOR ART
[0004] U.S. Patent No. 4,364,571, issued December 21, 1982, to Hershey, discloses a mechanical
seal assembly using a "GRAFOIL" (trademark) gasket or packing 28 positioned in an
annular recess formed between a gland 19 supporting a seal ring 31 and an insert 26,
the packing 28 being exposed to product fluid causing the packing to lose its resiliency
after substantial usage, presumably because it becomes filled with the fluid.
[0005] U.S. Patent No. 4,386,785, issued June 7, 1983 to Back, discloses a bellows mechanical
seal arrangement in which a retaining flange 6 holds a seal ring 5 in contact with
a seat 3, the bellows providing a resilient force to the flange 6.
THE INVENTION
[0006] According to the invention herein disclosed, it is proposed to provide an improved
mechanical seal assembly utilizing corrosive resistance materials and a secondary
laminated gasket between a seal ring and its supporting structure for high temperature
applications. The gasket is preferably being made of a graphite material generally
sold under the name "GRAFOIL" to thus overcoming the temperature limitations of elastomeric
gaskets, and further to avoid the concerns of a loose lap joint. The gasket provides
a positive connection of a seal ring made of a hard, non-weldable material, such as
silicon carbide, tungsten carbide and the like, to a seal ring supporting structure
or flange constructed of a high temperature, corrosion resistant alloy, such as 316
stainless steel, Hastelloy C and the like, capable of enduring the relatively elevated
temperatures contemplated and use with corrosive fluids. The gasket is preferably
constructed of a plurality of stacked washer or washer-like wafers or plates of GRAFOIL
and thus possesses a natural resiliency. In addition to the gasket, an attachment
ring generally of the same metal as the supporting structure or flange, is welded
to the high temperature and corrosion resistant metal alloy supporting structure.
This attachment ring is employed to make an integral assembly of supporting structure,
gasket, seal ring and attachment ring. In the construction according to this invention,
the gasket is positioned in an annular recess or pocket defined by the seal ring and
its supporting structure. This construction insures that the gasket is substantially
protected from exposure to process fluid, so that it will retain its resiliency for
a considerable length of time during its use and, because of its resiliency, will
urge the seal ring into intimate contact with the attachment ring.
[0007] Preferably, a metal bellows constructed of welded together metal washer-like plates
or members is welded at one end to a seal ring supporting flange and to a bellows
flange at the other end. The bellows flange is drivingly connected to the rotatable
shaft of the fluid handling apparatus, or, if the seal assembly is constructed as
a cartridge, to a shaft sleeve which encircles the shaft and provides a driving connection
therewith. The bellows resiliency urges the seal ring connected thereto toward the
opposing seal ring, so that their faces engage one another. The bellows provides a
driving connection between the shaft or the shaft sleeve, as the case may be, and
the seal ring supporting structure.
[0008] A positive drive between the supporting structure and the supported seal ring is
provided by an anti-rotational pin which extends from the supporting structure into
a suitable opening in the seal ring.
[0009] Alternatively, the bellows can be fixed to the housing, so as to urge the non-rotatable
seal ring toward the rotatable seal ring.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010]
Fig. 1 is an axial, partial sectional view of a mechanical seal assembly constructed
according to this invention; and
Fig. 2 is an enlarged sectional view of a portion of Fig. 1 showing the features of
this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0011] Looking now at the drawings, and especially Fig. 1, there is illustrated a mechanical
seal assembly 10 associated with a multiple part housing 12 and a rotatable shaft
14, the shaft 14 being connected at one end to a motor (not shown) and at the other
end to a fluid handling device, such as a pump and the like (not shown). The mechanical
seal assembly 10 functions to substantially prevent product fluid being handled by
the fluid handling device from leaking along the shaft to the motor or bearing system
to the atmosphere.
[0012] The mechanical seal assembly comprises a seal ring 16 connected to the housing 12
by a drive pin 18 fitting into a slot 20 in the housing 12. Thus the seal ring 16
is a non-rotatable seal ring. The seal ring 16 which may be constructed of carbon
graphite, silicon carbide, tungsten carbide, a ceramic and the like, has a lapped,
radially oriented, and annular seal face 22.
[0013] The seal assembly further comprises a seal ring 24 connected by means of a retainer
assembly 26, a bellows 28, an annular bellows flange 30, and a drive pin 32 to a shaft
sleeve 34 engaging the rotatable shaft 14. Positive connecting means (not shown) may
be use to insure the driving connection between the shaft sleeve 34 and the shaft
14. Thus the seal ring 24 is rotatable with the shaft 14. The seal ring 24 is preferably
constructed of a non-weldable material, such as silicon carbide or tungsten carbide,
has a lapped, radially oriented, and annular seal face 36 which opposes and contacts
the seal face 22 of the seal ring 16. When the shaft 14 is rotating, the seal faces
22 and 36 of the seal rings 16 and 24 contact and rotate relative to one another.
[0014] As illustrated in Fig. 1, the mechanical seal assembly is constructed as a cartridge
by using the shaft sleeve 34 which encircles the shaft 14 and rotates therewith. The
shaft sleeve 34 may be omitted, if necessary and/or desirable without affecting the
inventive concept of this invention. However, when the seal assembly is constructed
as a cartridge, repair and/or replacement of the assembly is simplified because the
assembly can be removed from the fluid handling apparatus as a unit and is easily
replaced as a unit, reducing down time of the fluid handling apparatus.
[0015] Looking from left to right in Fig. 1, the bellows 28, is preferably constructed of
a plurality of annular metal plates welded together in an integral structure, as known
in the prior art. The bellows is welded at one end to the bellows flange 30 and at
its opposite end to a seal ring support flange 38 of the retainer assembly 26. As
previously explained, the bellows 28 provides a resilient force to urge the seal ring
24 toward the seal ring 16. When assembled, the bellows 28 is compressed to some degree
to permit it to function as an axial force producing element.
[0016] The seal ring flange 38, see especially Fig. 2, has a radial portion 40 and a cylindrical
portion 42, the portion 42 having an inner diameter substantially equal to the outer
diameter of the seal ring 24. The seal ring 24 is provided with a reduced diameter
rear portion 44 and a reduced diameter forward portion 46. The cylindrical portion
42 of the flange 38 has an axial length substantially equal to the axial length of
the seal ring 24 minus the axial length of the forward portion 46. The flange 38 and
the reduced diameter rear portion 44 of the seal ring 24 form an annular recess, cavity
or pocket 48 which receives a gasket 50, preferably constructed of stacked washer
or washer-like wafers or plates of a graphite material sold under the name "GRAFOIL".
Because of the laminations, the gasket 50 possesses limited resiliency, and becomes
slightly compressed during assembly of the seal ring-retainer flange, as will be explained.
[0017] A retaining ring member 52 is welded, as at 54, to the cylindrical portion 42 of
the flange 38 and is constructed of such size and dimensions to fit onto the reduced
diameter forward portion 46 of the seal ring 24. The ring member 52 functions to maintain
the seal ring 24 in the flange 38 with the gasket 50 providing, because of its limited
resiliency, a seal against substantial leakage of process fluid into the interface
of the seal ring 24 and its supporting flange 38. Also the use of a lap joint is avoided;
the outer diameter of the seal ring 24 substantially matches the inner diameter of
the flange 38, without the critical fit of a lap joint. Suitable precautions are taken
during the assembly of the seal ring and the flange 38 to insure a substantial fit
of the ring 24 in the flange 38, as explained hereinafter.
[0018] A single drive pin 54 extending from the radial portion of the flange 38 and into
a pocket 56 in the seal ring 24 insures a positive drive between the shaft 14 and
the seal ring 24.
[0019] The procedure for installing the seal ring 24 into the flange 38 is as follows:
1. The pin 54 is inserted into the flange 38 before assembly of the flange with the
seal ring.
2. The gasket 50 is installed onto the seal ring and then the flange is heated by
induction heating to expand the flange to receive the seal ring 24.
Alternatively, the seal ring can be press fitted into the supporting flange avoiding
the induction heating step.
3. The retaining ring member 52 is installed onto the seal ring and against the flange.
4. Pressure is applied to the retaining ring member 52 to seat ring 52 against the
flange and to compress the gasket 50.
5. The retaining ring member 52 is welded to the flange 38 while applying pressure
as in step 4.
6. The assembly is tested for leakage into the gasket.
[0020] Applicant has thus provided an improved mechanical seal assembly which can us high
temperature, corrosion resistance alloys for a supporting flange for a hard, non-weldable
seal ring, without using non-reliable mechanical interference fits or lap joints between
the seal ring and its supporting flange.
[0021] The appended claims are intended to cover all reasonable equivalents and are to be
interpreted as broadly as the prior art will permit.
1. A mechanical seal assembly for sealing a rotatable shaft to a housing and the like,
comprising:
a pair of seal rings, at least one of which is connected for rotation with said shaft
and the other of which is non-rotatable and connected to said housing, one of said
seal rings being arranged for limited axial movement relative to said shaft;
said seal rings having radial seal faces opposing and engaging one another, one seal
face being rotatable with respect to the other seal face;
means resiliently urging one of said seal rings axially toward the other seal ring;
a seal ring retaining and supporting flange surrounding one of said seal rings; and
a retaining ring connected to said flange for retaining said seal ring in said surrounding
retaining and supporting flange,
2. A mechanical seal assembly for sealing a rotatable shaft to a housing and the like,
comprising:
a pair of seal rings, at least one of which is connected for rotation with said shaft
and the other of which is non-rotatable and connected to said housing, one of said
seal rings being arranged for limited axial movement relative to said shaft;
said seal rings having radial faces opposing and engaging one another, one seal face
being rotatable with respect to the other;
means resiliently urging one of said seal rings axially toward the other of said seal
rings;
one of said seal ring being formed of a relatively hard and non-weldable material;
a seal ring retaining and supporting flange surrounding said hard and non-weldable
material seal ring;
a high temperature resistant laminated gasket between said hard and non-weldable material
seal ring and said supporting flange; and
a retaining ring abutting said hard and non-weldable material seal ring and welded
to said retaining and supporting flange for retaining said hard and non-weldable material
seal ring in said flange.
3. A mechanical seal assembly as recited in Claim 2, wherein said hard and non-weldable
material seal ring is constructed of silicon carbide and said flange and retaining
ring are constructed of a corrosion resistant metal alloy.
4. A bellows mechanical seal assembly for sealing a rotatable shaft to a housing and
the like, comprising:
a pair of seal rings, at least one of which is connected for rotation with said shaft
and the other of which is connected to said housing, said rotatable seal ring being
arranged for limited axial movement relative to said shaft;
said seal rings having radial seal faces opposing and engaging one another, one seal
face being rotatable with respect to the other;
bellows means connected to said rotatable seal ring and urging said rotatable seal
ring axially toward the other seal ring;
at least one of said seal rings being formed of a relatively hard, non-weldable material;
a seal ring retaining and supporting flange surrounding said hard material seal ring;
means defining a cavity between said hard material seal ring and said flange;
a high temperature resistant laminated gasket in said cavity; and
a retaining ring welded to said flange for retaining said hard, non-weldable material
seal ring in said flange.
5. A bellows mechanical seal assembly as recited in Claim 4, in which said laminated
gasket is constructed of a plurality of stacked annular wafer-like members, and providing
a resilient structure, said gasket being compressed in said cavity and resiliently
urging said hard material seal ring toward said retaining ring.
6. A bellows mechanical seal assembly as recited in Claim 5, in which said hard material
seal ring is the rotatable seal ring, and further comprising the bellows welded at
one end to the flange and connected at its opposites end to said shaft.
7. A bellows mechanical seal assembly as recited in Claim 6, further comprising a
positive drive connection between said rotatable seal ring and said flange and thus
said bellows and said shaft, said positive drive connection comprising a drive pin
projecting from said flange and received in a groove in said rotatable seal ring.
8. A mechanical seal assembly for sealing a rotatable shaft to a housing and the like,
comprising:
a pair of seal rings, one of which is connected for rotation with said shaft and the
other of which is connected to said housing, said rotatable seal ring being arranged
for limited axial movement relative to said shaft;
said seal rings having radial sealing faces opposing one another, one seal face being
rotatable with respect to the other seal face;
resilient means urging said rotatable seal ring axially toward the other seal ring;
at least one of said seal rings being formed of a relatively hard and non-weldable
material;
a seal ring retaining and supporting flange surrounding said hard material seal ring,
said flange having a radial portion;
a high temperature resistant gasket between said seal ring and said radial portion
of said flange; and
a retaining ring welded to said flange for retaining said hard material seal ring
in said flange and against said gasket.
9. A mechanical seal assembly as recited in Claim 8, wherein said hard and non-weldable
material comprises silicon carbide.
10. A mechanical seal assembly as recited in Claim 9, wherein said seal ring supporting
and retaining flange and said retaining ring are constructed of a corrosion resistant
stainless steel.
11. A cartridge mechanical seal sub-assembly comprising:
a cylindrical sleeve adapted to encircle a shaft;
a seal ring surounding said sleeve and connected thereto for limited axial movement
relative thereto;
a flange surrounding said seal ring and having a radially extending portion at one
end;
a resilient means connected at one end to said sleeve and at the other end to said
seal ring flange, said resilient means providing the connection between said seal
ring and said sleeve;
a resilient high temperature resistant gasket between said flange portion and said
seal ring; and
a retaining ring welded to said flange at the end opposite the radially extending
portion and abutting said seal ring.
12. A cartridge mechanical seal sub-assembly as recited in Claim 11, further comprising
an annular cavity formed in said seal ring and partly defined by said flange, said
cavity receiving said gasket.
13. A cartridge mechanical seal sub-assembly as recited in Claim 11, further comprising
an annular reduced portion at one end of said seal ring to receive said retaining
ring.
14. A cartridge mechanical seal sub-assembly as recited in Claim 12, further comprising
an annular reduced portion at one end of said seal ring to receive said retaining
ring.
15. A cartridge mechanical seal sub-assembly as recited in Claim 11, in which said
seal ring is constructed of a non-weldable material and is surrounded by said flange.